Editorial policy and sourcing

This page explains where the numbers on this site come from and how they are checked, so you can decide how much to trust them.

Size data

All size pages are generated from one data table. For each thread, the table holds the major diameter and pitch, the calculated hole for 75% thread, the nearest standard drill and the thread percentage it gives. Inch threads use the tap makers' formula with the 0.01299 constant; metric threads use diameter minus pitch and the matching metric formula (OSG Tapping Guide, Vol. 3).

The calculated drill is then compared with independent published tap charts. A size is marked as confirmed when two charts agree with it. Where charts disagree, the page names both values and explains which one we chose and why. Pipe thread drills are checked against up to three charts, because those disagree most often.

Pilot hole sizes for wood screws and lag screws come from published charts and are compared with the lead-hole guidance in the USDA Forest Products Laboratory, Wood Handbook (2021), ch. 8. Lag screw pages show a range because the published charts do not agree.

Guides

Guides are researched from primary or near-primary sources, in this order of preference:

1. Tool and fastener makers' technical data (for example OSG, Tapmatic, Missouri Carbide, Kennametal, Walton).
2. Standards documents or their published tables (ASME, ISO).
3. Government and university references, such as the USDA Forest Products Laboratory Wood Handbook and university machine shop materials.
4. Established engineering references and trade publications such as Cutting Tool Engineering.

Every factual claim links to its source in the list at the foot of the guide. Where sources disagree, the guide says so instead of picking one silently. Worked examples are calculated and checked against published values.

Tools we use

The site is built with software that generates pages from the data table. We use computer tools, including AI writing and image tools, to help draft text and create illustrations. Every number is calculated from the formulas above and checked against the sources, and every page is reviewed before publication. Photographs on the site are illustrations made for it; they show typical tools rather than specific products.

Independence

The site earns money from ads and Amazon affiliate links. Advertisers and retailers have no say in content, and we do not accept payment for placement or reviews. Product links are to general Amazon searches for the tool a job needs, not to paid recommendations.

Corrections and updates

Email [email protected] with the page and the value in question. We check each report against sources and correct confirmed errors promptly. The footer of every page shows the date of the current revision.